Strategic loci on the hemoglobin molecule, such as the N-termini of the alpha and beta chains, will be chemically modified with derivatives of pyridoxal. In this way the oxygen affinity of hemoglobin will be modulated over a wide range. A specific reagent which crosslinks the beta chains at the polyphosphate binding site, i.e., 2-nor-2-formylpyridoxal 5' phosphate, will serve as a powerful tool for investigating the role of subunit dissociation in such reactions as cooperative ligand binding and conformational change, the hemoglobin-haptoglobin reaction, the copolymerization of HbS with other hemoglobins and many others. As part of a study of the polymerization of deoxy HbS we will institute a search for the contact points between the hemoglobin tetramers within the helical polymer. In addition to chemical modifications such as described above, hybrids will be prepared containing beta S chains and mutant alpha chains with substitutions which are known to be near the surface of the tetramer. We will also continue our study of hemoglobin molecules composed of four identical subunits. Finally, we shall investigate the linkage between proton and organic phosphate binding to hemoglobin both theoretically and experimentally. In addition, we propose to study the properties of some new allosteric effectors in which sulfate esters replace the normal phosphate ones.